The patients have been selected to the given therapy solely on the basis of geography. All patients treated with evacuation of primary chronic subdural hematoma(CSDH) from 2005 through 2010 at St.Olav University Hospital and UNN, and primary CSDH from 2006 through 2010 at Karolinska University Hospital (not 2005 due to practical reasons since major changes occurred in electronic surgery protocols 2005).